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your Main/Key light is always expessed as 1
your Highlighs are always expressed to the left of the of the Main/Key
which gives you an expression of 4:1 3:1 2:1 etc.
and your shadows are expressed to the right of the Main/Key
1:2 1:3 etc

So if you have a Main ,Fill and Hightlight/Accents
you might see this

2:1:2 which is F16,F11,F8

There is very little Info on this part of the Ratios listed on the internet
but there is a conflict

Last edited by Derek_Alvarez; 09-07-2006 at 12:59 PM.

“The price of anything is the amount of life you exchange for it.” Henry David Thoreau

Thanks for the diagram Kirk
If you look at Kirk's diagram it says 3:1 ratio. The 3 expresses the value of the Main light and is to the left of the 1. Now I'm not sure about the dome thing. A human face is in a dome shape so I would think that is what you would want to use to meter it. Not a flat 2 dimensional diffuser. I would think the only time to use the flat diffuser would be for a reflective reading or an incedent reading on a flat surface. But that's another can of worms.

Deb I would really love it if you could post the question as written for the test. I think it would help us all to understand the answer of 1.5 stops difference better.

Now I've decided from this thread that my interpretation of a three to one ratio being a 1 stop difference between main and fill is wrong (According to the book). But I have yet to see anyone come up with a comprehensive and clear cut explaination of a 3:1 ratio on this thread. How sad. We are CPPs Masters and Veterans of years of experience and something as basic as Ratios still draws conflicting conclusions. This is a testimony to the way we as an industry have allowed the basics to slip away from us. In a world of "If it feels good do it" photography the fundamental skills are being forgotten.

Thank you Deb for the wake up call and thank you everyone who contributed to this thread. You've all given me alot to chew on.

Thanks for the diagram Kirk
If you look at Kirk's diagram it says 3:1 ratio. The 3 expresses the value of the Main light and is to the left of the 1. Now I'm not sure about the dome thing. A human face is in a dome shape so I would think that is what you would want to use to meter it. Not a flat 2 dimensional diffuser. I would think the only time to use the flat diffuser would be for a reflective reading or an incedent reading on a flat surface. But that's another can of worms.

David, that "3:1" in the diagram is a typo on my part. It should be "1:3" as I've learned it.

As I was taught, it was a shadow illumination:highlight illumination ratio--not a fill light:main light ratio. That's why it comes out 1:3 instead of 1:2. If it were mere fill light:main light, it would merely be an expression of the bare difference in power--stops, watt seconds, watts, whatever. But because it's a ratio of the illumination that actually strikes the subject, it includes the additive effects of overlapping lights.

Derek is adding a number for the accent lights, too, and although I can't recall seeing that expressed, it's certainly valid.

Deb I would really love it if you could post the question as written for the test. I think it would help us all to understand the answer of 1.5 stops difference better.

Yep.

Now I've decided from this thread that my interpretation of a three to one ratio being a 1 stop difference between main and fill is wrong (According to the book). But I have yet to see anyone come up with a comprehensive and clear cut explaination of a 3:1 ratio on this thread.

I just gave it to you. It's the ratio of the shadow illumination compared to the highlight illumination, taking into account that the highlight illumination is a combination of both the fill light and the mainlight. It is not a ratio of the power of the lights (at least not as far as getting the question right on the PPA exam is concerned).

--Elephants can swim......and very gracefully. Knowing that, I do believe Anything is possible for me.

Bless you Karen
I would have gotten that wrong before Deb posted this thread. I would have assumed it meant how many F stops difference do you set between your Main and your Fill. Now because 1 is not an option I might have figured out 1.5 as being the brightest highligt compared to the shadow side. As for the 1:3 - 3:1 confusion It seems however you learn it will work if you remeber the order, but it seems easier to remember the set up if you think of 1 as the fill (less) and 3 as the main (more). If I tried to think of my main as 1 and my fill as 3, I would get mixed up and think my fill needed to be brighter than my main. So for the test my answer would have been wrong. Now in the real world when I've set my Main to F8 and my Fill to F5.6 I am creating a 3:1 ratio, and yes the meter will read 8.6 or so in the brightest highlight. So I'm doing it right I just didn't know how to explain it. What can I say Thanks again everyone! Old dogs can learn new tricks